Manufacture of methacrylic acid



July 3, 1945. L, CQES1 JR- 2,379,625

MANUFAGTURE OF METHACRYLIG` ACID l Filed Aug. 1e, 1940 v 2 sheets-sheet1 o c: o QfFFrCHZgI-H';

gva/www0@ L Dfw/v5 EUE5JH.

WM l WM July 3, 1945. GOES, JR 2,379,625

MANUFACTURE OF METHACRYLICACIDv Filed Aug. 1e, 1940 2 sheets-sheet 2CH3-COQHjEHQQHMHCHB-cog cHzff H o CH3 CH3 @HCD-ww l (|:H3 CLH-CofCHa(cHfocoa'cmz Hce+ z CHZr-clz-COQH CQ Cea L 7H/N5 E055 JR.

-ffrcw' Patented July 3, 1945 Aaazaszs MANUFACTURE oF METHACRYLIC ACIDLoring Coes, Jr., Brookiield, Mass., assignor, by mesne assignments, toE; I. du Pont de Nemours & Company, Wilmington,

Delaware Del., a corporation of Application August 16, 1940, Serial No.352,935

4 Claims.

The invention relates tothe manufacture of methacrylic acid and itsesters.

One object of the invention is to provide a simple process for makingmethacrylic acid. Another object of the invention is to provide a cheapprocess for making methacrylic acid. Another object of the invention isto provide a process for the manufacture of methyl methacrylate viapreparation of methacrylic acid which shall be as cheap as or cheaperthan any method heretofore known. Anotherrobject of the invention is toprovide a cheap way of obtaining other derivatives f methacrylio acid,for example besides the methyl ester, ethyl, propyl and butyl and otheralkylesters, also phenol esters, `metal salts, the anhydride of theacid, and many other derivatives of methacrylic acid. Another object isto' provide a process of the type indicated free from 1 the use ofdangerous or poisonous chemicals.

Other objects will be in part obvious or in party pointed outhereinafter.

The invention accordingly consists in the combinations of elements,arrangements of parts, and in the several steps and relation and orderof each of said steps to one or more of the others thereof, all as willbe illustratively described herein, Vand the scope of the application ofwhich will be indicated in the following claims.

In the accompanying drawings illustrating an important step in two ofmany possible embodiments of my invention:

In Figures 1, 2 and 3 are chemical equations showing three reactionsinvolvedin one method according to the present invention;

Figures 4, 5, 6 and '7 are chemical equations showing the reactionsinvolved in another method according to the present invention.

As `a starting material, I use methyl ethyl ketone. In the cracking ofpetroleum, butanol 2 is produced. From this, methyl ethyl ketone can bereadily manufactured in a well known manner.v Methyl ethyl ketone infairly pure form is readily available on the market and as of thepresent date has a price around ve cents a pound.

Other ingredients used in my process are formaldehyde, chloride of lime,hydrochloric acid, and a small amount of sulphuric acid. Formaldehyde isinexpensive, being at present about seven cents per pound in a 40%solution in water. Ordinary bleaching powder is good enough chloride oflime and this at present has a price of about two cents a pound.Hydrochloric acid costs about two cents a. pound and sulphuric acid, ofwhich little is used; about one cent a pound. Therefore, the ingre- (Cl.26o-531) dients in the manufacture of methacrylic acid according to thepresent invention are all linexpensive. For the manufacture of methylmethacrylate, the most valuable product to be derived from the acid,methyl alcohol is used which is still relatively inexpensive, costing atpresent about live cents a pound.

Considering now in detail the manufacturev of the acid, I take 500 gramsof methyl ethyl ketone, 3'75 grams of 40% formaldehydesolution in water,and 10 cc. of 2 normal sodium hydroxide. I cool it to below 30 C. andlet it stand for 24 hours. I distill this mixture and collect thefraction, boiling between 90 C. and 120l'C. at 20 millimeters ofmercury. This is beta methyl gamma keto butanol.

This is the rst `step inthe process and the re-V actionmay be indicatedas follows:

This reaction per se` however, is not novel.

The second step in the'total process which is.

believed to be novel, as awhole, may be carried out as follows: I take2'75 grams of commercial bleaching powder (an impure chloride of limeAVcontaining 33% of available chlorine) and suspend it inV 800 cc. ofwater. I then add a solution of 40 grams of the foregoing beta-methylgamma keto butanol inv 40 grams of water. The addition should be madegradually and the mixture should be stirred for about two hours atbetween 30 and 50 C.

To the foregoing mixture I then add 150 co. of concentrated hydrochloricacid, keeping the temperature below 50 C. I then heat the mixture toapproximately C. for one hour and then extract continuously with ethylether. The ether extract is then distilled to drive 01T the ether andthere remains methacrylic acid with some impurities. The methacrylicacid can be purified in known manners or else in the impure -form it canbe esterified to methyl methacrylate and the latter can be purified inknown manners.

In carrying out the second step' in the process, I provide a quantity ofcopper or other suitable linhibitor to prevent polymerization of themethacrylic acid during its manufacture. I believe the reactions willdefinitely convert all of the beta methyl gamma keto butanol tomethacrylic acid, and the thing to bev particularly guarded against ispolymerization of the methacrylic acid. Since the reaction may proceedat low temperatures and polymerization is slower at low temperatures,Vit

is possible to obtain a relatively high yield of methacrylic acid inmonomeric form. The use of copper as an inhibitor is a distinct aid incarrying out this step of the process. Other inhibitors which can beused are hydroquinone and pyrogallol.

In the foregoing, commercial bleaching powder has been selected as it isthe cheapest of the group consisting of the alkaline earth hypochloritesand alkali hypochlorites that I know of. The process, however, can becarried out using an alkali hypochlorite such as sodium hypochlorideNaOCl. Other alkali metals can be substituted, so also other alkalineearth metals. Also other halogens can be substituted for the chlorine.However, so far as I know, there is no advantage in using anything butthe cheapest.

Other acid hydrolyzing and dehydrating agents besides HC1 .can be used,for example, sulphuric acid and phosphoric acid.

It does not seem necessary to describe esterification of methacrylicacid to methyl methacrylate since this is now well known. Equally othermonohydric alcohols can be used to obtain the corresponding esters ofmethacrylic acid and, in fact, other products ,can be made from it, suchas the salts. By adding acetic anhydride, the anhydride of methacrylicacid can be produced. As set forth in co-pending application of Carl E.Barnes, Serial No. 326,974 led March 30', 1940, a hard transparent resinhighly useful for optical purposes, for windows and especially forairplanes, can be produced by copolymerizing methyl methacrylate with asmall quantity of methacrylic anhydride.

Referring now to the accompanying drawings, Figure 1 shows ahalogenation reaction in which beta methyl gamma keto butanol isconverted to delta delta delta trichloro beta` methyl gamma ketobutanol. At the same time, three molecules of calcium hydroxide areformed. The delta delta delta trichloro beta methyl gamma keto butanolimmediately breaks down, as shown in Figure 2, in a chloroform reaction,producing two molecules of chloroform and a molecule of calciumbeta'hydroxyisobutyrate. The reaction indicated in Figure 3 producesmethacrylic acid, calcium chloride and water. This weak acid isliberated by treating the salt with a strong acid and dehydration occursat the same time.

Other haloform reactions could be substituted for that shown in Figure 2if for the hypochlorite a. hypohalite having a halogen other thanchlorine were selected.

A similar process for the manufacture of methacrylic acid within thescope of the present invention is illustrated in Figures 4 to '7inclusive. Figure 4 illustrates the dehydrating of beta methyl gammaketo butanol to methyl isopropenyl ketone. As shown in Figures 5 and 6,this is then 'reacted with a hypohalite (using bleaching powderpreferably) to produce calcium methacrylate which is then, as shown inFigure '7, reacted with a strong acid to produce the methacrylic acid.In the reaction shown in Figure 5,

calcium hydroxide and trichloro-methyl isopropenyl ketone are producedfrom the calcium hypochlorite and methyl isopropenyl ketone. In thereaction shown in Figure 6 calcium methacrylate and chloroform areproduced from the calcium hydroxide and trichloro-methyl isopropenylketone. As an example of this embodiment of the invention, I may take 40grams of beta methyl gamma keto butanol, put it in a flask and warm itwith 10 cc. of hydrochloric acid. I then add sodium carbonate toneutralize the HC1 and then proceed as in the first example. However,from the -metal methacrylate the esters may be made directly.

It will thus be seen that there has been provided by this inventionmethods and compositions of matter in which the various objectshereinabove set forth together with many thoroughly.

practical advantages are successfully achieved. As various possibleembodiments might be made of the chemical features of the aboveinvention and as the art herein described might be varied in variousparts, all without departing from the scope of the invention, it is tobe understood that all matter hereinbefore set forth or shown in theaccompanying drawings is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. In the process of producing methacrylic acid, the steps comprisingreacting beta methyl gamma keto butanol and a hypohalite from the groupconsisting of alkaline and alkaline earth metal hypohalites, in anaqueous medium and, thereafter, treating said reaction mixture with anacid dehydrating agent from the group consisting of concentratedhydrochloric, sulfuric and Vphosphoric acids.

2. In the process of producing methacrylic acid, the steps comprisingreacting beta methyl gamma keto butanol and calcium hypochlorite in anaqueous medium and, thereafter, treating said reaction mixture withconcentrated hydrochloric acid.

3. In the process of producing methacrylic acid, the steps comprisingreacting beta methyl gamma keto butanol and a hypohalite from the groupconsisting of alkaline and alkaline earth metal hypohalites, in anaqueous medium for at least about two hours at 30 C.-50 C. and,thereafter, adding to the reaction mixture an acid dehydrating agentfrom the group consisting of Iconcentrated hydrochloric, sulfuric andphosphoric acids, and maintaining said reaction mixture at about '75 C.for at least about one hour.

4. In the process of producing methacrylic acid, the steps comprisingreacting beta methyl gamma keto butanol and calcium hypochlorite in anaqueous medium for at least about two hours at 30 C.-50 C. and,thereafter, adding concentrated hydrochloric -acid to the reactionmixture and maintaining said reaction mixture at about C. for at leastabout one hour.

LORING COES, JR.

